Plunger for mechanical pencils and method of producing same



Jan. 31, 1939. J. P. LYNN 2,145,459

PLUNGER F OR MECHANICAL PENCILS AND METHOD OF PRODUCING SAME I OriginalFiled June 27, 1936.

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Patented Jan. 31, 1939 UNITED STATES PATENT O PLUNGER FOR MECHANICALPENCILS AND METHOD OF PRODUCING SAME Melrose Park, 111., 2.

Original application J 87,705. Divided and corporation of Delaware nine27, 1936, Serial No. this application June 21,

1937, Serial No. 149,408

11 Claims.

This invention relates to an improved construction for plungers of thetype employed in certain mechanical pencils. The invention also re latesto a method of producing such plungers.

This invention is a division of applicants copending application SerialNo. 87,705, filed June 27, 1936, and patented July 20, 1937, Patent No.2,087,519.

In constructing certain types of mechanical pencils it is desirable incertain instances, to provide a lead guide tube formed as an open spiralwhich cooperates with a lead propelling plunger which is moved axiallywithin the tube by means of a portion which projects through the openspiral slot and engages with a longitudinal slot in the body of thepencil exteriorly of the spiral tube. With such constructions, relativerotation between the body of the pencil and the spiral serves to advanceor retract the plunger within the spiral tube.

For good operation, pencils of this type require a plunger which isaccurately held in axial alignment within the tube without liability oftilting or jamming when the plunger is advanced against a frictionallyheld lead. This is usually accomplished by forming the plunger frommetal stock which is of slightly less diameter than the interior of thetube whereby the plunger is free to slide axially in the tube while atthe same time being held by the tube in axial alignment. Plungers ofthis type further have a lateral extension which is preferably formedthereon by bending the wire or stock from which the plunger is formed.It has been found in practice, that when plungers of this type are madeof stock of such size as to be axially guided within the interior of thetube that then, the laterally formed portion of the plunger at thelocation of the bend, bulges somewhat, due to the excessive amount ofmetal at this location with the result that binding of the plunger inthe open spiral slot frequently occurs. Such lateral extensions alsousually have pitched surfaces at the top and bottom for contact with theedges of the spiral slot and a free camming and feeding action of theplunger by these pitched surfaces depends upon accurate alignment of theplunger in the tube. Thus ordinary plungers would frequently bind whenmade large enough to be held in alignment and would tilt and jam if madeof smaller stock.

Accordingly, it is an object of the present invention to provide a newconstruction of plunger which is free from the above named disadvantagesand which may be made by a simple and inexpensive process.

The plunger of this invention is characterized as composed of wire orred stock which is of substantially less diameter than the interiordiameter of the spiral guide tube with which it is to be associated.Thus with the diminished diameter, the formation of the lateralprojection for feeding the plunger does not involve the production ofthe unwanted bulging at the location of the bend. In order to maintainthe plunger in axial alignment in the tube, the body of the plunger isdeformed to provide a portion thereof with projecting bearing edgesconstituting means for holding and guiding the plunger in axialalignment within the tube.

This invention will be better understood by referring to theaccompanying drawing in which one illustrative embodiment of thisinvention is given and in which,

Figure 1 is a cross sectional View of a pencil of the open spiral typeembodying a plunger constructed in accordance with this invention, and

Figure 2 is an enlarged lateral view of the plunger constructed inaccordance with this invention and,

Figure 3 is an end view of the plunger illustrated in Figure 2, and

Figure 4 is a fragmentary view partly in cross section taken on thelines li of Figure 2 and looking in the direction of the arrows.

By referring to the drawing it will be noted that this invention isillustrated as embodied in a pencil having a tip Ill, a body ii, and aspiral guide tube H3. The spiral guide tube is held within the body bymeans of a bearing it so that the same is rotatable therein while heldagainst axial displacement. Within the spiral tube is a plunger E5, theconstruction of which is better shown in Figures 2 and 3. This plungeris formed with two diameters, the end diameter 22 of which issufficiently small to project into the lead receiving opening 23 at theextreme tip of the pencil without destroying the frictional pressureprovided at the pencil tip and the larger diameter 2% is of such size asto freely slide within the guide tube without undue wobbling or withoutliability of tilting or becoming misaligned from the axis of the tube.

This plunger is preferably formed of wire stock of diametersubstantially less than the inside diameter of the tube and the bodyportion it thereof is preferably formed by a swedging or similaroperation carried out in a punch press or equivalent machine. It is thepurpose of this invention to deform an amount of material constitutingthe body of the plunger to provide supporting bearing edges forengagement with the larger diameter of the interior of the lead guidetube. Although any desired shape may be selected, it is preferable toform the body with a triangular cross section because this provides athree point support. While forming the body portion as above described,the head end of the plunger 25 may likewise be formed into rectangularor other cross-sectional shape such as will better prepare the plungerfor the subsequent bending operation with the avoidance of the unwantedbulging at the location of the bend. Where a rectangular formation isgiven to the head the flat surface 26 thereof may be continuous with oneof the flat surfaces of the triangular portion. The head of the plungermay then be formed by bending the upper end to provide a laterallyextending member 27 for engaging the slot of the spiral tube I3 and thegroove 2| in the pencil body.

It will be noted from Figure 2 that the upper and lower surfaces 28 and29, respectively, of the lateral extension which engage with the edgesof the open spiral slot are pitched to conform to the pitch of thespiral, or in other words, so as to produce a lateral extension which isrhomboidal in cross section. These pitched surfaces enable the plungerto be freely and smoothly cammed in the slot to advance and retract theplunger in both directions in the tube. The head of the plunger also maybe formed with a tail piece 29 provi ing additional bearing surfaces inthe groove 2| obviously such tail pieces are not necessary.

Although any order of steps for forming the above described plunger maybe employed with good results, it has been found in practice that theplunger may be conveniently made by first swedging on a punch press orother suitable machine, the triangular body portion 24 by successiveoperations on a continuous rod of stock. After or simultaneously withthe formation of the triangular body portion, the rectangular head maybe formed by a similar swedging operation. The plungers may next besuccessively cut from the rod of stock and thereafter the head formed oneach by a bending operation which by means of dies also forms thepitched surfaces 28 and 29.

From the foregoing it will be apparent that this invention provides aplunger which has a free and easy camming action within the open spiraltube for advancing the lead as distinguished from plungers heretoforeused which are subject to jamming in the spiral due to the tilting andmisalignment of the plunger within the tube or to a binding of theplunger in the spiral slot because of a bulging of the metal at the headforming bend.

I claim:

1. The process of making a plunger which consists in swedging a portionof round wire stock into a non-round cross section to provide bearingedges lying on the circumference of a circle having a diameter greaterthan the diameter of said round wire stock and swedging a flat sideadjacent one end thereof and bending the end of said stock in thedirection of said fiat side to form a head on said plunger.

2. The process of making a plunger which consists in swedging a portionof round wir-e stock into a non-round cross section to provide bearingedges lying on the circumference of a circle having a diameter greaterthan the diameter of said round wire stock and swedging a fiat side adofthe body of the pencil but jacent one end thereof and bending the end ofsaid stock in the direction of said flat side to form a head on saidplunger, and during said bending operation, forming upper and lowerinclined surfaces on said head.

3. The process of making a plunger which consists in swedging a piece ofround wire stock so as to form a triangular body portion and arectangular head portion with one flat side of said rectangular portionformed as a continuation of and of substantially the same width as oneof the flat sides of said triangular body portion and thereafter bendingsaid head portion toward said fiat side to form a laterally projectinghead, and simultaneously with said bending forming cam surfaces on theupper and lower sides respectively of said head.

l. A plunger of the character described composed of wire stock having around lead abutting end and a body portion having spaced bearing edgeslocated on the circumference of a circle of diameter greater than thediameter of said round lead abutting end, and a head for said plungerextending later-ally from said body portion and being provided withinclined upper and lower cam surfaces.

5. A plunger of the character described composed of Wire stock having around lead abutting end and a body portion having spaced bearing edgeslocated on the circumference of a circle of diameter greater than thediameter of said round lead abutting end, and a head extending laterallyfrom said body portion and having substantially a rhombcidal crosssection.

6. A plunger of the character described composed of wire stock having around lead abutting end and a body portion having spaced bearing edgeslocated on the circumference of a circle of diameter greater than thediameter of said round lead abutting end, and a head extending laterallyfrom said body portion and having substantially a rhomboidal crosssection, and a tail for said head extending parallel to the axis of saidplunger from the end of said laterally extending head.

7. A plunger of the character described composed of wire stock having around lead abutting end and a body portion having at least one fiatsideand further having spaced bearing edges located on the circumference ofa circle of diameter greater than the diameter of said round leadabutting end and a laterally extending head projecting in the directionof said flat side of said body portion and having inclined top andbottom cam surfaces.

8. A plunger of the character described composed of wire stock having around lead abutting end and a body portion of triangular cross sectionhaving its edges located on the circumference of a circle of diametergreater than the diameter of said round lead abutting end and alaterally extending head projected in the direction of one of the flatsides of said triangular body portion and having inclined top and bottomcam surfaces.

9. A plunger of the character described composed of wire stock having around lead abutting end and a body portion of triangular cross sectionhaving its edges located on the circumference of a circle of diametergreater than the diameter of said round lead abutting end, and a headhaving a laterally extending portion, and a longitudinally extendingportion, said laterally extending portion having inclined top and bottombearing surfaces.

10'. A plunger of the character described composed of wire stock havinga round lead abutting end and a body portion of triangular cross sectionhaving its edges located on the circumference of a circle of diametergreater than the diameter of said round lead abutting end, and a headhaving a laterally extending portion, and a longitudinally extendingportion, said laterally extending portion having substantially arhomboidal cross section and said longitudinally extending portionhaving substantially a rectangular cross section.

11. A plunger of the character described composed of wire stock having around lead abutting end and a body portion of triangular cross sectionhaving its edges located on the circumference of a circle of diametergreater thanthe diam-eterof said round lead abutting end, and a headhaving a laterally extending portion and a longitudinally extendingportion, said laterally extending portion having substantially arhomboidal cross section and said longitudinally extending portionhaving substantially a rectangular cross section, a flat side of saidlongitudinally extending portion being disposed in opposed relation to aflat side of said triangular body portion and an inclined surface ofsaid laterally extending portion joining said flat surfaces.

JOHN P. LYNN.

